RARA

Acute promyelocytic leukemia

Gene mutations can be acquired during a person's lifetime and are present only in certain cells. These mutations are called somatic mutations, and they are not inherited. A somatic mutation involving the RARA gene causes acute promyelocytic leukemia, a cancer of the blood forming tissue (bone marrow). Acute promyelocytic leukemia is characterized by an accumulation of promyelocytes in the bone marrow. A rearrangement (translocation) of genetic material between chromosomes 15 and 17, written as t(15;17), fuses part of the RARA gene on chromosome 17 with part of another gene on chromosome 15 called PML. The protein produced from this fused gene, the PML-RARα protein, functions differently than the protein products of the normal PML and RARA genes.

The PML-RARα protein binds to DNA and represses gene transcription, like the normal RARα protein. However, the PML-RARα protein does not respond to the signal to induce transcription of genes, so the genes remain repressed.

Additionally, the function of the PML protein, the product of the PML gene, is disrupted. The PML protein blocks cell growth and division (proliferation) and induces self-destruction (apoptosis) in combination with other proteins. However, the PML-RARα protein does not block proliferation or induce apoptosis.

The PML-RARα protein blocks the differentiation of blood cells at the promyelocyte stage and allows abnormal cell proliferation. As a result, excess promyelocytes accumulate in the bone marrow and normal white blood cells cannot form, leading to acute promyelocytic leukemia.